As various properties required for automobile pneumatic tires, a reduction of rolling resistance, a stability on wet road surfaces and the like are demanded. In a method of allowing simultaneous achievement of the reduction of rolling resistance and the stability on wet road surfaces as described above, silica is compounded as a reinforcing filler in a rubber composition for tires.
However, when silica is compounded into a rubber composition for tires, silica is poorly dispersed into such composition. Therefore, even if a large amount of silica is added, effects thereof may not be fully achieved. This may pose a problem.
Patent Document 1 describes a rubber composition for treads comprising silica and polyethylene glycol compounded in a diene based rubber, in which 10 mass % or more of the diene based rubber is replaced with a styrene/isoprene/butadiene terpolymer. Patent Document 1 also describes that this rubber composition balances wet performance with rolling resistance at a high level, and further describes that the composition shows good processability when kneading.
As an attempt for improving various properties required for automobile pneumatic tires, a method is also proposed in which a modified diene based polymer obtained by graft- or block-modifying a diene based polymer with a specific compound is added to a rubber composition for tires.
Patent Document 2 proposes that a diene based polymer obtained by block- or graft-copolymerizing polyethylene glycol diglycidyl ether to a diene based elastomer as a functionalizing agent is added to a diene based polymer in order to allow interactions with a reinforcing filler, for example, silica, carbon black and the like. A reinforced rubber composition obtained in this way shows improved hysteresis characteristics in a vulcanized state when the vulcanization is performed for tires, specifically treads for tires, by the reinforced rubber composition, and maintains satisfactory processing characteristics in a non-crosslinked state.